Washington — Senators grilled Pentagon officials Wednesday about the new US strategy for countering Islamist extremism in Afghanistan and Pakistan, pressing them on whether President Obama was committing enough troops to the fight and how America would measure progress in the region.

While lawmakers indicated general support for the new plan, unveiled March 27, some see the administration’s postponement of key decisions about troop levels as evidence that the strategy is still a work in progress.

They asked Gen. David Petraeus and others about the need to identify a target size for the Afghan army and police, and tried to probe why the president did not deploy to Afghanistan the full number of forces requested by Gen. David McKiernan, the top commander in Afghanistan.

Mr. Obama is boosting the US force in Afghanistan by about 21,000, on top of the 7,000 additional troops former President Bush had ordered to the country. But General McKiernan’s request for another 10,000 troops won’t be decided on until later this year, General Petraeus and other defense officials acknowledged this week.“If the troops were needed, would they be sent?” asked Sen. Mel Martinez (R) of Florida.

The answer: Time-lines presented to Obama allow him to make a decision later this year that could put additional forces in Afghanistan in 2010. Unspoken but implied: A force of 10,000 simply may not be available now because of commitments in Iraq. Petraeus emphasized that the Afghanistan mission requires more than just military forces, anyway.

“While additional military forces clearly are necessary in Afghanistan, they will not by themselves be sufficient to achieve our objectives,” said Petraeus. “It is important that the civilian requirements for Afghanistan and Pakistan be fully met as well.”

A bigger Afghan force sought

Besides the added US forces, Obama’s new strategy relies on a “surge” of civilian expertise and a more defined focus on defeating extremism in the region. It also calls for a larger Afghan army – widely seen as a crucial ingredient to success in Afghanistan – but does not prescribe a specific size for the army or police.

The Afghan army is expected to grow from 90,000 to 134,000 by the end of 2011. The police force is close to reaching its 82,000 target, but many officers need retraining and, perhaps, replacement. The size of both forces should total about 400,000 in the next several years, some experts and lawmakers say.

“We know that [a larger force] was a vital element to our success in Iraq, and to dribble out these decisions, I think, can create the impression of incrementalism,” Sen. John McCain (R) of Arizona told Petraeus and other administration officials at Wednesday’s hearing before the Senate Armed Services Committee.

“The word ‘incremental’ is a bit too harsh, but [McCain’s] overall points, especially about the Afghan forces, are still generally correct,” he says. “Then again, so is the general thrust of Obama’s policies – even if the goals aren’t yet ambitious enough.”

Obama’s strategy may be vague about the target size of the Afghan army as American officials negotiate for more resources from allies this week in Europe, some analysts say.

A fast troop buildup

A contingent of about 70,000 US and NATO forces is already on the ground in Afghanistan. With fresh US forces now arriving and 21,000 more soon to come, logistical challenges loom large. The US and its allies will need to build up bases and airstrips to support them.

Indeed, the US runs the risk of sending too large a force too fast, says Seth Jones, a political scientist at the RAND Corp. Besides, he says, the size of the Afghan military or the buildup of American forces is not necessarily the most important issue right now. Instead, the US must think about what incentives it will use to co-opt militants and turn them against the Taliban.

“That is a much bigger issue,” he says. The president’s Afghanistan-Pakistan plan “is not specific on how to do that.... There is a very broad statement, but it is pretty vague on how to do it and when.”

Strategy aside, concern exists in and outside the military that the US and its allies still don’t have an objective way of measuring success. Top military officials testified recently that the information in Afghanistan is far too “anecdotal” to be used effectively.

Lawmakers Wednesday echoed the concern.

“How will we assess whether the new strategy is working? How will we know if we’re winning?” asked Sen. Susan Collins (R) of Maine.